Treating all the volumes to remove the mold would cost $1.8 million, the Columbia Daily Tribune reported Tuesday.
"We don't have that," Jim Cogswell, the libraries' director, said.
Cogswell said the top priority is saving older books, those printed before 1870.
The problem is a result of trying to save money, Cogswell said. The library system began storing books at Subtera, an underground storage facility in north Columbia after running out of space. The mold problem was discovered in October.
"We are in this predicament because we had to find a cheap alternative place to put our books in," Cogswell said. "We were required to find cheap alternatives to essentially rent storage space because our library is underfunded compared to every other library of our size."